"Artificial leaves – recently profiled by the New Yorker – resemble a thin playing card, described by MIT as a "silicon solar cell with different catalytic materials bonded onto its two sides". Covered with water and placed in sunlight, it splits hydrogen and water, mimicking photosynthesis.
In a real leaf, the hydrogen is then combined with CO2 from the atmosphere to make sugars, cell walls and other organic matter. In the artificial version, scientists use the hydrogen in fuel cells to make electricity or else combine it with CO2 to make fuels such as methanol. This could be used in car engines, much as ethanol biofuels are used today and would provide a carbon-neutral source of power."